Many companies do just fine with the standard, off-the-shelf smartphones that can be picked up from any carrier, but many need something different. For this reason, unprovisioned-or unlocked-devices are gaining interest, if not widespread availability, at this time.
One thing you should know is that unprovisioned smartphones are only a subset of unlocked phones. It is possible to buy an unlocked phone that is provisioned for a specific carrier but that can have its provisioning changed to some other carrier. Other unlocked smartphones are completely unprovisioned.
Provisioning a phone really means telling the phone what network it should be running on for data access. When you put a SIM card into a GSM smartphone, that provisions the phone for a specific voice carrier. However, you also need to tell the phone the addresses of the network routers it should use, how and where it should get its IP address, and the like. You may also need to tell the device what to do if it finds multiple voice networks and multiple data networks available.
Provisioning is normally done through a series of menu choices in the phone's system settings. However, with some phones, it's possible to create a script that will perform the task for you. In many cases, the carriers will provide the scripts for the most commonly used smartphones. T-Mobile, for example, keeps a library of smartphone provisioning scripts on its Website.
The availability of unlocked phones is likely to increase along with greater scrutiny into deals between carriers and device makers that lock customers into exclusive contracts.
A primary example of a deal being examined by the Federal Communications Commission is the one in which Apple's iPhone is available in the United States only from AT&T. This forces U.S. users who want to go with another carrier to either unlock the AT&T phone (and risk having it relocked by Apple when the phone is connected to iTunes) or to import an iPhone from Germany to get a T-Mobile version.
Congress also has its eye on these kinds of deals and, at the very least, could make such exclusive deals easier to bypass. This may mean that carriers may soon be willing to provide unlocked versions of devices that currently are not available in that form.
There are currently several smartphones that are available as unlocked devices.
The Palm Pro, for example, is available only as an unlocked device. Its 3G features work only with AT&T in the United States, although it can be provisioned to work with most 3G carriers elsewhere. Likewise HP's Windows Mobile 6.1-based iPaq 910c is available only as an unprovisioned, unlocked smartphone. You'll have to get a SIM card from your carrier and then set up the phone manually. In addition, Nokia makes several of its smartphones available as unlocked devices.
You can also buy devices in an unlocked form even if their manufacturers don't provide them that way in the United States, but there may be risk. For example, you can buy unlocked BlackBerrys even though Research In Motion doesn't sell them that way, but generally these phones are sold by third parties without a warranty.